The present invention relates to a network relay device (layer 2 switch) configured to relay data in a layer 2 network and a relevant network relay method.
IGMP snooping (Internet Group Management Protocol snooping) and MLD snooping (Multicast Listener Discovery snooping) is the known technique to relay a multicast frame with high efficiency in a layer 2 network. In order to prevent flooding of a multicast frame by a layer 2 switch, the IGMP/MLD snooping technique allows the layer 2 switch to snoop a message sent from a host joining a multicast group to a router, learn the transfer destination of the multicast frame and store the learning result in the form of snooping information in the layer 2 switch.
In the event of a communication failure in the layer 2 network adopting the IGMP/MLD snooping technique, there are two possible actions taken by the layer 2 switch. The first action stops relay of the multicast frame, in order to prevent flooding, until the snooping information is re-learnt according to a change in network configuration accompanied by the occurrence of the communication failure. The second action allows flooding of the multicast frame, in order to prevent non-delivery of the multicast frame. In order to shorten the recovery time between the occurrence of a communication failure and relearning of the snooping information, one proposed technique causes the layer 2 switch to send a multicast receiver search message that searches for a node intended to receive multicast packets, in response to detection of the communication failure.